The present invention relates to making inflatable protective cushions, and more specifically relates to the type of curtain cushion particularly useful in side protection of occupants in a transportation vehicle, such as an automotive vehicle, railroad, car, airplane, or the like.
Inflatable protective cushions used in passenger vehicles are a component of relatively complex passive restraint systems. The main elements of these systems are: an impact sensing system, an ignition system, a propellant material, an attachment device, a system enclosure, and an inflatable protective cushion. Upon sensing an impact, the propellant is ignited causing an explosive release of gases filling the cushion to a deployed state that can absorb the impact of the movement of a body against it and dissipate its energy by means of rapid venting of the gas. The entire sequence of events occurs within about 30 milliseconds.
A typical construction material for airbags has been a polyester or, nylon fabric, coated with an elastomer such as neoprene, or silicone. The fabric used in such bags is typically a woven fabric formed from synthetic yarn by weaving practices that are well known in the art. In the un-deployed state, the cushion is most commonly stored in or near the steering column, the dashboard, in a door panel, or in the back of a front seat placing the cushion in close proximity to the person or object it is to protect.
The use of a coating material has found acceptance because it acts as an impermeable barrier to the inflation medium. This inflation medium is generally a nitrogen or helium gas generated from a gas generator or inflator. Such gas is conveyed into the cushion at a relatively warm temperature. The coating obstructs the permeation of the fabric by such gas, thereby permitting the cushion to rapidly inflate without undue decompression during a collision event.
Airbags may also be formed from uncoated fabric that has been woven in a manner that creates a product possessing low permeability or from fabric that has undergone treatment such as calendaring to reduce permeability.
Silicone coatings typically use either solvent-based or complex, two-component reaction systems. Dry coating weights for silicone have been in the range of about 3 to 4 ounces per square yard or greater for both the front and back panels of side curtain airbags.
The majority of commercially used restraint cushions are formed of woven fabric materials utilizing multifilament synthetic yarns of materials such as polyester, nylon 6 or nylon 6,6 polymers.
The driver-side airbags are typically of a relatively simple configuration in that they function over a fairly small well-defined area between the driver and the steering column. One such configuration is disclosed in U.S. Pat. No. 5,533,755 to Nelsen et al., issued Jul. 9, 1996, the teachings of which are incorporated herein by reference. However, inflatable cushions for use in the protection of passengers against frontal or side impacts must generally have a more complex configuration since the position of a vehicle passenger may not be well defined and greater distance may exist between the passenger and the surface of the vehicle against which that passenger might be thrown in the event of a collision.
As will be appreciated, the permeability of a side cushion airbag structure is an important factor in determining the rate of inflation and subsequent rapid deflation following the impact event. In order to control the overall permeability of the cushion, it may be desirable to use differing materials in different regions of the cushion. Thus, the use of several fabric panels in construction of the cushion may prove to be a useful design feature. The use of multiple fabric panels in the cushion structure also permits the development of relatively complex three-dimensional geometries that may be of benefit in the formation of cushions for passenger side applications wherein a full-bodied cushion is desired. While the use of multiple fabric panels provides several advantages in terms of permeability manipulation and geometric design, the use of multiple fabric panels for use in passenger side restraint cushions has historically required the assembly of panels having multiple different geometries involving multiple curved seams.
Panel geometries that include curved seams-pose a problem for permeability. Curved seams tend to leak inflation medium to a greater degree than seams following or perpendicular to the warp of the fabric. Consequently, side curtain airbags are designed and oriented so that the longest straight seam is parallel to the warp of the fabric.
As will be appreciated, another important consideration in cutting panel structures from a base material is the ability to maximize the number of panels which can be cut from a fixed area through close-packed nesting of the panels. It has been found that minimizing the number of different geometries making up panels in the cushion and using geometries with substantially straight line perimeter configurations generally permits an enhanced number of panels to be cut from the base material with the least waste. The use of panels having generally straight-line profiles has the added benefit of permitting the panels to be attached to one another using substantially straight seams or to be substantially formed during the weaving process using a jacquard or dobby loom. For the purposes of this invention, the term “seam” is to be understood as any point of attachment between different fabric panels or different portions of the same fabric panel. Thus, a seam may be sewn (such as with thread), welded (such as by ultrasonic stitching), woven (such as on a jacquard or dobby loom, as merely examples), and the like. Substantially straight seam configurations thus provide more cost-effective methods of producing airbags.
Technology has been developed to improve the impermeability of curved seams. For example, see Sollars, Jr., in U.S. Pat. No. 6,220,309, issued Apr. 24, 2001, teaching an inflatable fabric comprising basket-woven attachment points between fabric panels; Li et al in U.S. Pat. No. 6,451,715, issued Sep. 17, 2002, teaching a low permeability side curtain airbag having extremely low coating levels; and Li et al, U.S. Pat. No. 6,429,155, issued Aug. 6, 2002, teaching low permeability airbag cushions having film coatings of extremely low thickness, all of which are incorporated herein by reference.
Side curtain airbags not only provide cushioning effects from impact but also provide protection from broken glass and other debris. They also help to restrain a passenger during vehicle roll over. Upon inflating, side curtain airbags tend to contract. Contraction increases tension and their ability to restrain passengers from lateral movement, and especially when the vehicle they occupy is rolling over with the windows open. As such, it is imperative that side curtain airbags, retain large amounts of gas, at high gas pressures, to provide restraint and cushioning throughout the longer time periods of the entire potential rollover situation, and contract as much as possible to provide the restraint needed to hold the passengers in the vehicle.
There is thus a need for a method of making a strongly contracting airbag that increases the number of airbags that can be made from a unit area of fabric while not significantly contributing to inflation medium leakage.